1. Field of the Invention
The invention pertains to the field of processing of biosolids. More particularly, the invention pertains to pathogen inactivation in biosolids such as sludge.
2. Description of Related Art
Today, the process of sludge treatment for the purpose of pathogen reduction involves the addition of various high pH materials, such as lime, for pathogen inactivation. The addition of the high pH materials can take place in either the liquid stream or the dry form. Commonly, lime is added to a low speed (e.g. 60 RPM) auger that is mixing dried sludges or just simply added to the sludge. The mixture is then allowed to sit for 12 hours to allow pH and heat to reduce the number of pathogens. However, these processes do not cause a direct physical impact on the pathogens themselves.
Variations on this process have tried to solve the problem of lowering the level of pathogens in sludge. For example, Nicholson""s xe2x80x9cMethod of Treating Wastewater Sludge,xe2x80x9d U.S. Pat. No. 4,781,842, issued in Nov. 1, 1988; Nicholson et al.""s, xe2x80x9cMethod for Treating Wastewater Sludge,xe2x80x9d U.S. Pat. No. 4,902,431, issued Feb. 20, 1990; Burnham""s xe2x80x9cProcess to Stabilize Wastewater Sludge,xe2x80x9d U.S. Pat. No. 5,275,733, issued on Jan. 4, 1994; Burnham""s xe2x80x9cMethod for Treating Wastewater Sludge,xe2x80x9d U.S. Pat. No. 5,135,664, issued Aug. 4, 1992; Angell et al""s, xe2x80x9cPathogenic Waste Treatment,xe2x80x9d U.S. Pat. No. 5,482,528, issued Jan. 9, 1995; and Angell et al""s, xe2x80x9cPathogenic Waste Treatment,xe2x80x9d U.S. Pat. No. 5,422,015, issued Jun. 6, 1995 all utilize a pH shift to induce pathogen destruction.
Another example of solutions to lowering the pathogens in sludge is Haley et al""s, xe2x80x9cApparatus and Method For Treating Waste Sludge,xe2x80x9d U.S. Pat. No. 5,419,839, issued May 30, 1995; Christy et al""s, xe2x80x9cProcess for Treating Sewage Sludge,xe2x80x9d U.S. Pat. No. 5,186,840, issued Feb. 16, 1993; and Haley et al""s, xe2x80x9cApparatus and Method for Treating Waste Sludge,xe2x80x9d U.S. Pat. No. 5,409,605, issued Apr. 25, 1995; all describe mixing chambers that utilize slow augers to add an alkaline substance to cause a pH shaft which will in turn cause pathogen destruction.
The third example of solutions to lowering the pathogens in sludge is Kew et al.""s, xe2x80x9cApparatus for Treatment of Waste Water Sludge,xe2x80x9d U.S. Pat. No. 5,240,599, issued Aug., 31, 1993; LeClair et al.""s, xe2x80x9cMethod and Apparatus for Producing Liquid Suspensions of Finely Divided Matter,xe2x80x9d U.S. Pat. No. 5,522,553, issued Jun. 4, 1996; and Kew et al.""s, xe2x80x9cMethod for Treatment if Waste Water Sludge,xe2x80x9d U.S. Pat. No. 5,282,980, issued Feb. 1, 1994, in these references the rotor/stator has been suggested as a means of treating sludges for the purpose of decreasing particle size and of aiding in dewatering, but it has not previously been considered as a means of either reducing pathogen numbers directly or of being used to introduce lime into the sludge stream as in the present invention.
The method of pathogen inactivation in biosolids with cavitation using the steps of processing the biosolids in a high-speed rotor/stator mill, digesting the resultant sludge, and adding an alkaline agent to the sludge while it is in a high-speed rotor/stator mill. The resultant treated sludge is then placed in a vessel for at least 12 hours to ensure that the high pH is maintained.